1. Field of the Invention
The present invention relates to a toroidal type continuously variable transmission which can be used, for example, as a transmission for an automobile. More specifically, the present invention relates to a toroidal type continuously variable transmission having means for absorbing the thrust load and the radial load applied to the output shaft and the input shaft.
2. Related Background Art
A toroidal type continuously variable transmission schematically shown in FIGS. 10 and 11 has been developed as the transmission for an automobile. In this toroidal type continuously variable transmission an input disk 2" (a first disk) is rotatably supported coaxially with an input shaft 1 (a first rotation shaft) as disclosed in Japanese Laid-Open Utility Model Application No. 62-71465, and so on. On the other hand, an output disk 4" (a second disk) is fixed at an end of an output shaft 3 (a second rotation shaft). Trunnions 6, which are rocked around their respective pivots 5, are set on the inner surface of the housing of the toroidal type continuously variable transmission or the trunnions 6 are supported by a support bracket provided in the housing. The pivots 5 are arranged in torsional or diagonal positions with respect to the input shaft 1 and the output shaft 3.
The pivots 5 are provided on both end portions of the side surface of each trunnion 6. The base portion of a shiftable shaft 7 is set at the center of each trunnion 6 so that the tilt angle of the shiftable shaft 7 can be controlled by rocking the trunnion 6 around the pivot 5. Power rollers 8' are rotatably supported around their respective shiftable shafts 7 supported by the trunnions 6. The power rollers 8' are pinched between the input disk 2" and the output disk 4".
The toroidal surfaces of the input disk 2" and the output disk 4", that is, the inner surfaces 2a and 4a thereof facing to each other are formed as concave surfaces having arched cross-section with centers that coincide with the axes of the pivots 5. Spherical peripheral surfaces 8a' of the power rollers 8' are in contact with the inner surfaces 2a and 4a.
Between the input shaft 1 and the input disk 2", a loading-cam type pressure device 9' is provided to elastically press the input disk 2" toward the output disk 4". The pressure device 9' comprises a cam plate 10 rotatable together with the input shaft 1 and a plurality of rollers 12' which are radially arranged and held by a holder 11. One side surface (the left side in FIGS. 10 and 11) of the cam plate 10 is formed as a cam surface 13' having circumferential projections and
recesses. A similar cam surface 14' is formed on the outer side surface (the right side in FIGS. 10 and 11) of the input disk 2".
At the time of operation of the toroidal type continuously variable transmission constructed as described above, the cam plate 10 is rotated in association with rotation of the input shaft 1 so that the cam surface 13' presses the plurality of rollers 12' against the cam surface 14' at the outer side of the input disk 2". Therefore, the input disk 2" is pressed against the power rollers 8' and simultaneously the cam surfaces 13' and 14' are engaged with each other through the plurality of rollers 12 to rotate the input disk 2". The rotation of the input disk 2" is transmitted through the power rollers 8' to the output disk 4" so that the output shaft 3 fixed to the output disk 4" is rotated.
In order to change the ratio of the rotating speeds of the input shaft 1 and the output shaft 3, for example, in order to decelerate the rotating speed of the output shaft 3, the shiftable shafts 7 are tilted to rock the trunnions 6 around their respective pivots 5 to the position shown in FIG. 10 where the peripheral surfaces 8a' of the power rollers 8' are in contact with the inner surface 2a at a portion close to the center thereof as well as with the inner surface 4a at a portion close to the outer periphery of the output disk 4".
On the other hand, when the rotating speed of the output shaft is accelerated, the shiftable shafts 7 are tilted to rotate the trunnions 6 to the state shown in FIG. 11 where the peripheral surfaces 8a' of the power rollers 8' are in contact with the inner surface 2a of the input disk 2" at a portion close to the outer periphery as well as with the inner surface 4a of the output disk 4" at a portion close to the center thereof. If the tilt angles of the shiftable shafts 7 are controlled intermediate between the two states shown in FIGS. 10 and 11, intermediate ratios of the rotating speeds of the input shaft 1 and the output shaft 3 can be obtained.
FIG. 12 shows a more concrete construction of a toroidal type continuously variable transmission for an automobile disclosed in Japanese Utility Model Application No. 61-87523 (Japanese Laid-Open Utility Model Application No. 62-199557). The rotation of the crank shaft of the engine is transmitted through a clutch 15 to an input shaft 16 to rotate a cam plate 10' which is engaged through splines with the middle part of the input shaft 16. A pressure device 9" including the cam plate 10' pushes an input disk 2'" toward an output disk 4'" (leftwards in FIG. 12) and rotates the input disk 2'". The rotation of the input disk 2'" is transmitted through power rollers 8" to the output disk 4'".
The output disk 4'" is supported around the input shaft 16 by a needle bearing 17, while a cylindrical output shaft 18 integrally formed with the output disk 4'" is supported inside a housing 19 by an angular ball bearing 20. One end (right end in FIG. 12) of the input shaft 16 is rotatably supported in the housing 19 by a roller bearing 21, while the other end thereof is rotatably supported in the housing 19 through a sleeve 23 by an angular ball bearing 22.
A transmission gear 26 comprising a forward drive gear 24 and a backward drive gear 25 integrally formed with each other is engaged with the peripheral surface of the output shaft 18 through splines. In order to drive the vehicle forward, the transmission gear 26 is shifted rightwards so that the forward drive gear 24 comes to be directly engaged with a forward driven gear 28 provided in the middle part of a take-out shaft 27. In order to drive the car back, the transmission gear 26 is shifted leftwards so that the backward drive gear 25 is engaged, indirectly through an intermediate gear (not shown), with a backward driven gear 29 fixed in the middle part of the take-out shaft 27.
When the toroidal type continuously variable transmission as constituted above is used, the input shaft 16 is rotated by an engine through the clutch 15 and the transmission gear 26 is moved in an appropriate direction so that the take-out shaft 27 is rotated in a given direction. The trunnions 6 are rocked and contact positions between the peripheries 8a" of the power roller 8" and the inner surfaces 2a and 4a of the input disks 2'" and 4'" are changed so that rotation speed ratio between the input shaft 16 and the take-out shaft 27.
At the time of operation of the toroidal type continuously variable transmission described above, the pressure device 9" presses the input disk 2'" toward the output disk 4'". As a result, the input shaft 16 supporting the cam plate 10' of the pressure device 9" is given a rightward thrust load in FIG. 12, which is the reaction force caused by the pressure of the pressure device 9". The thrust load is supported by the ball bearing 22 through a nut 30 threaded around the end of the input shaft 16, a disklike spring 34 and the sleeve 23. The pressure device 9" also generates a leftward thrust load in FIG. 12, which is transmitted through the input disk 2'", the output disk 4'" and the power rollers 8" to the shaft 18. This thrust load is absorbed by the ball bearing 20 through a stopper ring 33 fitted around the output shaft 18.
In FIG. 12, reference numeral 31 denotes a clutch for an engine brake and 32 denotes a direct coupling clutch. As the structure and functions of these components which are not included in the scope of the present invention are recorded in the above-mentioned Japanese Utility Model Application No. 61-87523 (Japanese Laid-Open Utility Model Application No. 62-199557), detailed description thereof is omitted.
In the conventional toroidal type continuously variable transmission concretely described above, the input shaft and the output shaft are not arranged coaxially but in parallel with each other. Power transmission means such as a Gear, a chain, and so on is provided between the output disk and the output shaft, which may inevitably increase the size and the weight of the toroidal type continuously variable transmission.
ThouGh the input shaft 1 and the output shaft 3 are coaxially arranged in FIGS. 10 and 11 which only illustrate the principle of the toroidal type continuously variable transmission, the radial load and the thrust load given to the shafts 1 and 3 can not be effectively supported in that arrangement. Accordingly, the construction shown in FIGS. 10 and 11 can not be practically applied to the transmission for an automobile because of many problems such as insufficient rigidity. The toroidal type continuously variable transmission according to the present invention was devised in order to solve such problems.